1. Field of the Invention
This invention relates generally to the art of radiation therapy and diagnostic imaging. More specifically, the invention relates to the use of contrast agents in therapy planning and treatment involved in radiation therapy.
2. Related Art
In the treatment of cancer and other diseases, therapeutic measures such as particle beam therapy are commonly employed. In particle beam therapy, a beam (or beams) of radiation in the form of electrons, or photons, or more recently, protons, is delivered to a tumor or other target tissue. The dosage of radiation delivered is intended to destroy the tumorous cells or tissues.
It is state of the art today that medical imaging techniques such as CT (Computed Tomography), MR (Magnetic Resonance), PET (Positron Emission Tomography), optical imaging (ultraviolet/infrared/visible) or ultrasound are used to visualize the target region (most often a tumor) for particle beam therapy. Yet, the medical imaging techniques used for this purpose in many cases cannot reliably differentiate between malign tumors and benign tumors, and in particular are not well suited to visualize exactly the borderline between healthy tissue and malign tumors. Thus the therapy control methods today are based on non-optimal medical images, and as a consequence, for the sake of a successful destruction of the tumor, the volume to be irradiated usually is chosen larger than absolutely necessary thereby damaging healthy tissue in the process. Exact positioning and dosage is especially critical in therapies that use proton beams, where the energy is highly concentrated in particular locations due to the well-know Bragg Peak phenomenon.
Additionally, it happens in many cases that the images used for therapy planning do not exactly show the location of the target tissue for irradiation during the therapy session, for example because the patient is not positioned exactly in the same way during the imaging and the therapy session, or because the filling of the intestinal tract is different in both sessions, and thus organs are shifted. The composition and relative thickness of fatty tissue, fluids, muscle, and connective tissue in the beam pathway needs to be known, and unfortunately, can change after therapy planning. Recently, artificial or anatomical landmarks are used to control the position of the target tissue.
One solution that has been used recently in some imaging techniques is the introduction of “contrast agents” which enhance the image quality achieved during imaging. To provide diagnostic data, the contrast agent must interfere with the wavelength of radiation used in the imaging, alter the physical properties of the tissue/cell to yield an altered signal or provide the source of radiation itself (as in the case of radio-pharmaceuticals). Contrast agents are introduced into the body of the patient in either a non-specific or targeted manner. Non-specific contrast agents diffuse throughout the body such as through the vascular system prior to being metabolized or excreted. Non-specific contrast agents may for instance be distributed through the bloodstream and provide contrast for a tumor with increased vascularization and thus increased blood uptake. Targeted agents bind to or have a specific physical/chemical affinity for particular types of cells, tissues, organs or body compartments, and thus can be more reliable in identifying the correct regions of interest.
Several different targeted contrast agents which bind to particular tissue and then exhibit signal changes based upon state changes in tissues (which are then imaged) are disclosed in international patent application WO 99/17809, entitled “Contrast-Enhanced Diagnostic Imaging Method for Monitoring Interventional Therapies”.
In particular, the dosage of energy that is planned for can often not be measured, determined or monitored very accurately. Further, even if the planned dosage of energy is delivered to a target tissue, it is not usually known until after treatment whether the treatment succeeded in destroying the target tissue.
The methods used today in monitoring of dosage and success in radiation therapy a in real-time during the therapy session, are sub-optimal and need to be improved.